Each one takes me under 15 mins usually...I believe the last one took me the longest (mostly because I was still a photoshop/lightroom newbie).
Hmm...the first one was just a conversion from color to Black&White in Lightroom. For the second one, I had to get rid of some wrinkles and spots on the white background. The white background was the back of wrapping paper, so it had a lot of winkles and some of the color on the wrapping paper was trying to show through. And on the third one (tulip and rose), I gave it some extra contrast and upped the vibrance.
Finally..the last one...I remember having to straighten the horizon. The faint mountains in the background where only on the left side of the tree originally. It looked really off balance and awkward, so I used the clone tool in Photoshop to add some mountains on the right side. I darkened some of the shadows in the snow (under the tree). There was also a bit of vignetting done on the top two corners. I used a dark blue instead of black to do the vignetting.